Semiconductors are used in integrated circuits for electronic applications, including radios, televisions, cell phones, and personal computing devices, as examples. One type of semiconductor device is a semiconductor storage device, such as a dynamic random access memory (DRAM) and flash memory, which use a charge to store information.
A recent development in semiconductor memory devices involves spin electronics, which combines semiconductor technology and magnetics. The spin of electrons, rather than the charge, is used to indicate the presence of binary states “1” and “0.” One such spin electronic device is a magnetic random access memory (MRAM) device, which includes conductive lines (wordlines and bitlines) positioned in different directions, e.g., perpendicular to one another in different metal layers, the conductive lines sandwiching a magnetic stack or magnetic tunnel junction (MTJ), which functions as a magnetic memory cell. A current flowing through one of the conductive lines generates a magnetic field around the conductive line and orients the magnetic polarity into a certain direction along the wire or conductive line. A current flowing through the other conductive line induces the magnetic field and can partially turn the magnetic polarity, also. Digital information, represented as a “0” or “1,” is storable in the alignment of magnetic moments. The resistance of the magnetic memory cell depends on the moment's alignment. The stored state is read from the magnetic memory cell by detecting the resistive state of the MTJ.
MRAM devices are typically arranged in an array of rows and columns, and the wordlines and bitlines are activated to access each individual memory cell. In a cross-point MRAM array, current is run through the wordlines and bitlines to select a particular memory cell. In a field effect transistor (FET) array, each MTJ is disposed proximate a FET, and the FET for each MTJ is used to select a particular memory cell in the array. In a FET array, an electrode is typically formed between the MTJ and the FET to make electrical contact between the MTJ and the FET.
An advantage of MRAM devices compared to traditional semiconductor memory devices such as dynamic random access memory (DRAM) devices is that MRAM devices are non-volatile. For example, a personal computer (PC) utilizing MRAM devices would not have a long “boot-up” time as with conventional PCs that utilize DRAM devices. Also, an MRAM device does not need to be continually powered to “remember” the stored data. Therefore, it is expected that MRAM devices will replace flash memory, DRAM and static random access memory devices (SRAM) devices in electronic applications where a memory device is needed.
Because MRAM devices operate differently than traditional memory devices and because they are relatively new, they introduce design and manufacturing challenges.